Heating elements are widely used in many fields and preferably characterized in having high fusing point, high resistivity and good oxidation-resistant property.
The commonly used materials for heating elements application are classified into four groups: (1) Ni-Cr or Ni-Cr-Fe alloys (2) Fe-Cr-Al alloys, (3) pure metals and (4) nonmetallic heat-element materials. The materials of the first group are most commonly used because they have good ductility and high resistivity and in addition, they can be used within a broad temperature range and in various atmospheres. Although the materials of the second group have a higher resistivity than that of the first group, their tensile strengths are relatively low. In addition, their microstructures become fragile after periodically thermally treated at a high temperature. Furthermore, the heating elements made of the second group become elongated so that their resistance is greatly changed after repeatedly heated. The materials of the third group are not widely applied because of the working atmosphere limitation. As for the materials of the fourth group, silicon carbide is cheap but fragile, graphite has a poor oxidation-resistant property so that it cannot be used at a temperature over 400.degree. C. in an oxidizing atmosphere, and molybdenum disilicide is suitable to be used for heating elements but is too expensive.
A conventional method used for manufacturing a Ni-Cr heating element is the ingot metallurgy technique which includes steps of refining crude metals to form an ingot, plastically working the ingot and manufacturing the desired product from the ingot by way of other further process, e.g. manufacturing a wire by way of wire drawing. So far, the cheapest and the most commonly used Ni-Cr heating element made by the conventional ingot metallurgy consists of 78.5% Ni, 20% Cr and 1.5% Si by weight. This kind of heating element has a microstructure of a solid solution and a fusion temperature of 1400.degree. C. and normally works at a temperature of 1150.degree. C.